Flexible Cycle Time-Optimized Sharing of a Working Space for Robots

ABSTRACT

The invention relates to a method and a system for controlling a robot, which non-simultaneously shares a working space with another robot. On the basis of a determined residual period, in which the working space remains occupied, the path planning of a robot is adjusted in a cycle time-optimized manner, in order to avoid a deceleration at the working space limit and a wait for the working space to be vacated.

This application claims the benefit of priority under 35 §119(a) toGerman Patent Application No. 10 2014 222 857.3, filed on Nov. 10, 2014.

1. TECHNICAL FIELD

The present invention relates generally to a method for controlling amanipulator, which shares a working space with at least one othermanipulator, and, in particular, wherein the working space is not usedsimultaneously by the manipulators.

2. TECHNICAL BACKGROUND

Manipulators, in particular industrial robots, are used for various workprocesses in, for example, assembly or production in industrialenvironments. Industrial robots are automatically controlled machinesequipped with three or more freely programmable movement axes, which areequipped with appropriate tools for the automatic manipulation ofobjects.

The use of several manipulators, for example, robots, which share thesame working space (or workplace, working range), can increaseproductivity. However, a working space should not be used by severalmanipulators at the same time, as this can lead to collisions. For thisreason, a manipulator or its controller checks, usually before it entersinto a defined common working space, at the limit of the working space,that the working space is not occupied and is thus vacant. If theworking space is not vacant, the manipulator conventionally deceleratesdirectly before reaching the working space limit. Only when the workingspace is vacated, does the manipulator accelerate again and enter intothe working space. This method has certain disadvantages, in particular,it leads to undesired manipulator down time. In addition, thedeceleration and acceleration consumes additional energy and increasesthe stress on the manipulator.

In the patent document US 2009/0204258 A1 published in the Englishlanguage on Aug. 13, 2009 and hereby incorporated by reference in itsentirety herein, a system and a method are described to control aplurality of robots on a rail. To prevent the robots from colliding, itis proposed to monitor dynamic spaces of the robots, and to halt a robotin the event of overlap of these spaces.

Furthermore, the patent document US 2013/0110288 A1 published in theEnglish language on May 2, 2013 and hereby incorporated by reference inits entirety herein, proposes modelling the working space of everyrobot, and defining one or more interference areas. The interferenceareas should be classified either as “prohibited”, “monitored” or“hybrid”. The status of a hybrid interference area is dynamicallytoggled for each robot between “prohibited” and “monitored”, dependingon whether the hybrid area is free of other robots.

The U.S. Pat. No. 7,765,031 B2, published in the English language onJul. 27, 2010 and hereby incorporated by reference in its entiretyherein, relates to a method for avoiding an interference between aplurality of robots in an overlapping section between occupation zonesof a plurality of robots. Furthermore, the patent specificationdescribes a robot which is able to avoid an interference with anotherrobot in an overlapping section between the occupation zones of therobot and of the other robot.

It is thus known from the prior art to identify working space violationsand, if necessary, to stop the movement of a manipulator, in order toavoid collisions.

In view of the above-explained prior art, the objective of the presentinvention is to provide a method and a system which permits better useof a working space by several manipulators, and thereby eliminates orminimizes the above-mentioned disadvantages. The objective is achievedwith the method according to claim 1 and the manipulator systemaccording to claim 10.

3. CONTENT OF THE INVENTION

The method according to the invention for controlling a manipulator, inparticular a robot such as an industrial robot, for instance, inparticular permits an efficient sharing of a working space with at leasta second manipulator. In principle, the method according to theinvention can be used when a plurality of manipulators are tonon-simultaneously share a working space. For the sake of simplicity,the following is based on the case of a working space which is shared bytwo manipulators not at the same time (non-simultaneously), i.e. theworking space may always only be used by one of the two manipulators atany given time. A first manipulator is initially located outside of theworking space, while a second manipulator first uses the working spaceor is located in the working space and thus occupies it. The twomanipulators each have prespecified, defined movement profiles (movementpatterns or movement sequences).

According to the method, real-time information about the actual statusof the movement profile of the second manipulator is supplied while thissecond manipulator is located in the working space. This real-timeinformation preferably comprises the position and the speed of thesecond manipulator. However, the real-time information can also contain,for example, data about forces and/or acceleration. It is particularlyadvantageous that the real-time information is supplied in real time, inother words, in a clock-synchronous manner.

In another step, there is determination, based on the supplied real-timeinformation and the prespecified movement profile of the secondmanipulator, of the residual period which the second manipulatorrequires in order to move out of the working space. In other words, theresidual period specifies the time period during which the working spaceremains occupied by the second manipulator. This residual period canpreferably contain the number of system cycles during which the secondmanipulator will remain in the working space.

In a subsequent step, the movement profile of the first manipulator,which is located outside of the working space, is adjusted in responseto the determined residual period. The movement profile is adjusted suchthat the first manipulator adjusts its movement into the working spacein such a way that halting of the first manipulator in front of theworking space is avoided. The remaining residence period of the secondmanipulator in the working space is thus responded to, so that the firstmanipulator enters into the working space at the earliest after expiryof the residual period, and does not halt at the limit of the workingspace beforehand and wait for it to be vacated. This permits a cycletime-optimized adjustment of the speed profile of the first manipulator.As the result of such an optimization of the cycle times, the efficiencyof the collaboration of several manipulators is improved.

Generally preferably, the adjustment of the movement profile of thefirst manipulator comprises a reduction of the speed, and/or a travel ona deceleration trajectory or an increase of the speed. Preferably, thefirst manipulator moves steadily without abruptly stopping or abruptlyaccelerating and reaches the working space at an optimal speed, whenthis working space is vacated. Such an adjustment of the movementprofile of the first manipulator, dependent on the remaining residenceperiod of the second manipulator located in the working space, saves onenergy and materials, as a deceleration and an acceleration at theworking space limit are avoided. Travel on a deceleration trajectorymeans that the manipulator travels a detour, so as to arrive at theworking space at a later point in time than was planned in the originalmovement profile. For example, the manipulator does not travel in adirect line to the working space, but instead travels in an arc. It isthus possible to reduce or avoid undesirable deceleration operations.

The adjustment of the movement profile is preferably based on theprespecified movement profile of the manipulator and comprises carryingout at least one other work step outside of the occupied working space.This means that the manipulator continues working on the basis of itsprespecified movement profile, in that it carries out, e.g., certainwork tasks or work sequences, which are pre-programmed into its movementprofile. Thus a work step, for example, which, according to theprespecified movement profile, is to be executed at a later point intime outside of the working space in question by the first manipulator,can be advantageously brought forward. This also prevents the firstmanipulator from halting at the working space limit and waiting for theworking space to be vacated.

The first manipulator preferably increases its speed when the timeinterval between the first manipulator and the working space limit isgreater than the determined residual period. In other words, if thefirst manipulator requires, according to its current path schedule, alonger period of time in order to reach the working space than theresidual period which the second manipulator still requires in order tomove out of the working space, the first manipulator increases its speedaccordingly, in order to advantageously minimize the time in which theworking space is not used.

It is also preferred that the first manipulator reduces its speed and/ortravels on a deceleration trajectory, when the time interval between thefirst manipulator and the working space limit is less than thedetermined residual period. In other words, if the first manipulatorrequires, according to its current path schedule, a shorter period oftime in order to reach the working space than the residual period whichthe second manipulator still requires in order to move out of theworking space, the first manipulator reduces its speed accordinglyand/or travels on a deceleration trajectory (i.e. a detour, forexample). Alternatively or in addition, the first manipulator can alsoexecute at least one other work step outside of the occupied workingspace. This ensures that the first manipulator enters into the workingspace in a continuous movement, once the second manipulator has movedout of it, without the first manipulator halting at the working spacelimit. By comparison with the methods which are known from the priorart, such adjustment of the speed profile achieves optimal utilizationof the manipulators and lower energy consumption is also preferablyachieved, and material fatigue is reduced.

The first manipulator and the second manipulator preferably each haveindependent controllers. Preferably, the second manipulator, which islocated in the working space, supplies the real-time information and/orthe determined residual period to the first manipulator, which islocated outside of the working space, only when at least one previouslydefined requirement has been satisfied. This ensures that the secondmanipulator does not continually supply the data to the firstmanipulator, but rather does so only at a determined point in time. Inthis way, the total data volume transferred is significantly reduced.Because less data is supplied, the workload of the first manipulator isalso reduced, since it has less data to analyze.

The previously defined requirement preferably involves falling short ofa previously defined residual period, which the second manipulatorrequires in order to move out of the working space. It is alsopreferable that the previously defined requirement involves fallingshort of a previously defined spatial distance between the secondmanipulator and the working space limit. It can thus be stated that thesecond manipulator supplies the real-time information and/or thedetermined residual period to the first manipulator only when it hasreached a certain spatial and/or time distance from the working spacelimit.

The manipulator system according to the invention, comprising twomanipulators, in particular industrial robots, which non-simultaneouslyshare a working space, is equipped with a control device, which isconfigured to execute the method according to the invention, so as to beable to implement the described steps of the method.

4. EXEMPLARY EMBODIMENTS

The invention is explained in greater detail below with reference to theaccompanying figures, in which:

FIG. 1 shows a robot cell with two robots in a purely schematic sketch;

FIG. 2 shows another robot cell with two robots; and

FIG. 3 shows a flowchart, which depicts, in a schematic and exemplarymanner, the sequence of the method according to the invention.

FIG. 1 shows a robot cell 100 having two collaborating manipulators,namely, two robots 110, 120. These robots 110, 120 are preferablyindustrial robots, which are mobile and which enter into working spacesand can move out of them again. The robots 110, 120 are controlled bymeans of appropriate control devices. According to the invention, therobots 110, 120 can each have independent controllers or they can have acommon controller. Also identified is a working space 130, which isnon-simultaneously shared by both robots. In other words, robot 110 canuse the working space 130 only when robot 120 has moved out of it. Ifrobot 110 were to enter into the working space 130 before robot 120 hasleft it, the risk of collision would be increased. For this reason, theworking space 130 should only be occupied by a maximum of one robot, soas to avoid possible collision. It is thus possible for robot 110 forexample to check at the limit of the working space 130, whether thisworking space is vacant. If this is the case, then the robot 110 canenter into the working space 130. If, however, robot 120 is in theworking space 130, or is working therein, robot 110 receives in responseto its check a signal that the working space 130 is occupied. Robot 110must therefore wait, until robot 120 has moved out of the range 130 andthus vacates it.

FIG. 2 likewise shows a robot cell 200, which has a working space 230,which is used non-simultaneously by two robots 210, 220. The two robots210, 220 are installed in a stationary manner, however they can reachinto the working space 230 by means of their robot arms. In a similarway to the above-described situation, here, robot 210 can move its ToolCenter Point (TCP) 211 into the working space 230 only when the TCP 221of the robot 220 is moved out of this working space. The person skilledin the art will understand that the robot 210 enters into the workingspace 230 only when robot 220 has completely moved out of it.

The present invention allows the robot 110, 210, which is locatedoutside of the working space 130, 230 and wants to use same, to react tothe current status of the other robot 120, 220, which is located insidethe working space 130, 230. The robots no, 120, 210, 220 haveprespecified movement profiles, which allow anticipatory cooperationbetween several robots. Through the supply of one or several items ofreal-time information, and the determination of the residual perioduntil an occupied working space is vacated, the working space 130, 230can be shared in a cycle time-optimized manner. Thus it is possible, forexample, for the robot no, 210 to reach the working space at optimalspeed, as soon as this working space is vacated.

FIG. 3 shows a sequence diagram for carrying out a method 3000 accordingto the invention. The method begins in step 3001. In this step 3001, theworking space or working range, which is not to be used simultaneouslyby several robots, is defined. The working space can have various forms,such as a Cartesian, cylindrical, or spherical form, for example.

At the outset, a first robot is located outside of the defined workingrange in step 3110, while a second robot is located inside the workingspace in step 3210. The starting position is thus similar, for example,to the situations depicted in FIG. 1 or FIG. 2, and can also be appliedto these or to similar situations.

One module of the controller of the second robot can formulaterequirements in step 3211, such as falling short of a time interval forthe second robot to reach the working space limit, for example. Theperson skilled in the art will understand that any number ofrequirements logically linked to one another can be formulated. In step3212, the second robot moves toward the working space limit, in order tomove out of the working space.

In decision 3213, it is determined whether the requirement formulated instep 3211 has been satisfied. If this requirement has been satisfied, instep 3214 an event is communicated in real time to the first robot. Thisevent can comprise, for example, real-time information about the actualstatus of the second robot. Alternatively or in addition, the event canalso involve the residual period in which the second robot is stilloccupying the working space. In this case, the second robot determinesthe residual period based on the real-time information about the actualstatus of its movement profile. It is then possible for the second robotto communicate to the first robot, for example, the number of systemcycles during which the second robot (according to the path schedule)will still remain in the working space. The second robot then moves outof the working space in step 3215.

The person skilled in the art will understand that the real-timeinformation about the actual status of the movement profile can containvarious data. The real-time information can thus include, for example,the position and speed of the robot, or of the TCP of a robot.Alternatively, this real-time information can also include data aboutforces, torques and/or accelerations. The real-time information does, inall cases, include such information as allows the determination, incombination with the pre-specified movement profile, of the residualperiod which a robot requires in order to move out of a working space.

The first robot, which is located outside of the working space at thepoint in time 3110, registers into events from the second robot in step3111. It can thus advantageously be stated that the first robot shouldreceive events from the second robot only from the time of thisregistering.

In step 3112, the first robot approaches the working space. In thedecision 3113 it is checked whether the first robot has already reachedthe working space limit. If this is the case, and if the working spaceis not vacant, the first robot halts in step 3114 and waits until thesecond robot is located outside of the working space, and this workingspace is thus vacant. This is a precautionary measure and should notoccur in normal situations, as halting of the first robot in normalsituations is prevented according to the invention. This is indicated inthe diagram by the dashed line.

If the first robot has not yet reached the working space limit, in step3115 it is checked whether an event was received by the second robot. Ifno event was received by the second robot, in step 3116 it is checkedwhether the first robot is executing the last command to enter into orto approach the working space. If this is the case, and the second robotstill has not received an event, a delay strategy is applied to thefirst robot in step 3117. A delay strategy can involve one or more ofthe following actions: halting, continued travel with reduced speed,travel on a deceleration trajectory, or carrying out at least one otherwork step outside of the working space.

If, however, it has been determined in step 3115 that an event wasreceived by the second robot, the data supplied by the second robot isanalyzed in step 3118. If, for example, real-time information about theactual status of the second robot was supplied, it is possible todetermine, based on this information and the prespecified movementprofile of the second robot, the residual period during which the secondrobot is still occupying the working space. Alternatively, the residualperiod can also have been determined by the second robot andcommunicated to the first robot.

In step 3119 it is determined whether one or more previously definedrequirements have been satisfied. Such a requirement could, for example,include that the time interval between the second robot and the workingspace limit, or the residual period which the second robot requires inorder to move out of the working space, is less than the time intervalbetween the first robot and the working space limit. If this is not thecase, a delay strategy, as described above, is applied to the firstrobot in step 3117. This allows the first robot to not reach the workingspace limit too early and means that it does not have to halt and waitthere.

Otherwise, if it was determined in step 3119 that the residual period ofthe second robot is less than the time interval between the first robotand the working space limit, the speed of the first robot is maintainedor preferably increased in step 3120. This ensures that the first robotadvantageously reaches the working space limit at precisely the timewhen the working space is vacated. Alternatively, the first robot canalso reach the working space limit shortly after the vacation of theworking space. The period of time during which the working space isunused or vacant is thus minimized. Finally, the first robot enters thevacant working space in step 3121.

The person skilled in the art will understand that not all of the stepsof the method 3000 must be carried out in order to allow a cycletime-optimized sharing of a working space as per the present invention.Alternatively, one or more steps can also be added. Thus the disclosedmethod can, for example, also include the first robot decelerating atthe working space limit and waiting for the working space to be vacated,if the second robot remains, contrary to the schedule, in the workingspace. As another variant, the second robot can send an additional eventto the first robot, when the second robot has definitely moved out ofthe working space. Furthermore, the method 3000 can, on the other hand,also be expanded to stipulate that more than two robots can share theworking space in a non-simultaneous and cycle time-optimized manner. Itshould be noted that the invention claimed herein is not limited to thedescribed embodiments, but may be otherwise variously embodied withinthe scope of the claims listed infra.

REFERENCE NUMERALS LIST

-   110, 120, 210, 220 Robots-   130, 230 Working spaces

1. A method for controlling a first manipulator, in particular a firstrobot, which non-simultaneously shares a working space with at least asecond manipulator, in particular a second robot, wherein the twomanipulators each have prespecified movement profiles, which methodincludes the following steps: a) supplying real-time information aboutthe actual status of the movement profile of the second manipulator,while it is in the working space; b) determining, based on the suppliedreal-time information and the prespecified movement profile of thesecond manipulator, of the residual period which the second manipulatorrequires in order to move out of the working space; c) adapting themovement profile of the first manipulator as a response to the residualperiod determined in step b), so that the first manipulator adjusts itsmovement to the limit of the working space in such a way that halting ofthe first manipulator in front of the working space is avoided.
 2. Themethod according to claim 1, wherein the real-time information comprisesat least one of a position, speed, force or torque.
 3. The methodaccording to claim 1, wherein the adjustment of the movement profile ofthe first manipulator comprises at least one of a reduction of a speedof the first manipulator, a travel on a deceleration trajectory or anincrease of the speed of the first manipulator.
 4. The method accordingto claim 1, wherein the adjustment of the movement profile is based onthe prespecified movement profile and comprises execution of a work stepoutside of the working space.
 5. The method according to claim 1,wherein the first manipulator increases its speed when a time intervalbetween the first manipulator and the working space limit is greaterthan the determined residual period.
 6. The method according to claim 1,wherein the first manipulator performs at least one of reducing itsspeed or traveling on a deceleration trajectory when the time intervalbetween the first manipulator and the working space limit is less thanthe determined residual period.
 7. The method according to claim 1,wherein the first manipulator and the second manipulator each haveindependent controllers and the second manipulator supplies thereal-time information and/or the determined residual period to the firstmanipulator only when at least one previously defined requirement hasbeen satisfied.
 8. The method according to claim 7, wherein thepreviously defined requirement involves at least one of falling short ofa previously defined residual period, which the second manipulatorrequires in order to move out of the working space, or falling short ofa previously defined spatial distance between the second manipulator andthe working space limit.
 9. The method according to claim 1, wherein theresidual period contains the number of system cycles during which thesecond manipulator will remain in the working space.
 10. A manipulatorsystem, comprising two manipulators, in particular robots, whichnon-simultaneously share a working space, and wherein the system isequipped with a control device, which is configured to execute a methodaccording to one of claims 1-9.